The present invention relates to perimetry and more specifically to an automated method and apparatus of kinetic perimetry.
A visual field chart is a contour map of a patient's field of vision. Visual field examinations are designed to test differential light sensitivity of the eye of a patient. The difference threshold is the smallest measurable difference in luminance between a stimulus (target) and a field of comparison (background). The results of such examinations are typically plotted on a visual field chart.
Testing the field of vision of a patient is important to ophthalmologists, neurosurgeons and others interested in diseases affecting the brain and visual system. The pattern of deviation from normal visual fields can be used by a physician to localize the lesion to a certain part of the eye or brain, help the determine the activity and prognosis of the disease process causing the defect and even suggest the precise diagnosis in some instances. Major causes of organic blindness, i.e. glaucoma, cataract, diabetes, other vascular diseases, uveitis, retinal detachment, senile vascular degradation, all have characteristic patterns of defect in the visual field, often showing these defects early in the disease process.
The ability to follow the progression of a disease process is an important function of visual field testing. This requires that testing be accurate and consistent. When the visual threshold values of a patient are measured, and those results are compared with those of normal subjects or of the same patient at an earlier time, an accurate, standarized, reproducible method of measurement must be available. The physical characteristics of the stimulation must thus be known and measurable. Regular standardization of the physical characteristics provides a guarantee for the reproducibility of the stimulation and is a first essential of visual field examinations.
Generally, visual field testing falls within two broad categories, kinetic and static perimetry. In kinetic perimetry a target is moved from a point outside the field of vision of the patient into the field of view of the patient. The patient responds when the target is first detected. In the case of static perimetry, targets are fixed spots that do not move but the size and/or intensity is increased until the patient sees the target stimulus.
Within these two general categories of perimetry, there are many approaches to visual field testing. Perhaps, the simplest is the "confrontation" test. Here, the examiner asks the patient to look at him and then brings his hand in from the side noting when the patient first sees it in his peripheral vision. This is a very crude form of kinetic perimetry.
Another simple form of kinetic perimetry is the tangent screen. This is a black felt cloth that is used to test the central 30.degree. field of vision. The cloth is generally hung on the wall one meter away from the patient. The examiner uses a black wand with white targets of different sizes on the end. The examiner monitors the patient's fixation as he moves the white target across the black screen. Small pins are stuck into the felt to outline isopters, a contour line within which a patient sees a target of given size and intensity. The visual field map is then transfered from the wall felt to a standard paper chart. This method is quite imprecise since there is no standardization of room light, target movement, target intensity, etc.
The best known of the kinetic perimeters is referred to as the Goldmann-type projection perimeter. This type perimeter is named after Dr. Hans Goldmann, a European ophthalmologist who did much of the original design and testing on the hemispherical bowl concept. Available Goldmann-type perimeters are manually operated. The operator selects the target (stimulus), size and intensity, moves the target within the bowl, monitors patient fixation and records responses on the chart. In some cases, automatic recording is provided which provides for automatic marking of the field of vision chart each time the patient presses the response button.
Since the movement of the target spot within the hemispherical bowl is manual, extensive training and practice under the guidance of a physician or experienced perimetrist is necessary for the operator to learn how to use the perimeter. This training may take up to a year to teach a technician the necessary skills. Manually operated Goldmann type perimeters also require full time involvement of the technician.
There are numerous types of static perimetry devices described in the literature and in the market. Some use hemispherical bowls as used in Goldmann-type perimeters. Others use flat, rectilinear screens. Still others use cathode ray screens for the projection of target spots. In some cases, the selection of the spot size and/or intensity, the location of the target spot size, and the recordation of when the target is seen by the patient is done automatically. In some cases, this is carried out by the use of a programmed computer. See, for example, U.S. Pat. Nos. 3,664,732, 3,718,386, 3,883,234, 3,705,003 and 3,172,404. However, the fixed location of the target sports in the case of static perimetry lends itself to the use of automatic control means such as a programmed digital computer.
Automatic kinetic perimetry has not heretofore been accomplished. The problem of being able to automatically direct the target scan so as to accurately and correctly determine the field of vision of a patient is an extremely difficult and complex task. The visual field of a patient who has an eye disease is often very irregular and contorted, thus making it extremely difficult to provide non-manual scanning to insure a correct visual field test.